Just like we have developer forum in SalesForce, i want to implement one in SalesForce, Have anyone implemented it ? If not, how to achieve it in SalesForce ? 

I want to display chatter to public, is this possible? Do i have to do a lot of coding in VF and APEX ? 

or

I want to make my community public, i,e., without actually logging in visitior should be able to see and traverse all the tabs available. Is this possible ? If so, how to achieve this ? 

I want to perform these steps,

1. Open a Web-Application (Custom, say, www.someWebApp.com).
2. Feed in Login credentials of Salesforce (in www.someWebApp.com's login page).
3. Validate these credentials in SalesForce.
4. If Valid user, take User to SuccessServelt.
5. If invalid user credentials, take user to FailureServelt.

Alternatively, i tried,
https://www.salesforce.com/us/developer/docs/api_rest/Content/intro_understanding_web_server_oauth_flow.htm

but, the 4th step is not clear, what exactly has to be done.

Please help.

Just like we have developer forum in SalesForce, i want to implement one in SalesForce, Have anyone implemented it ? If not, how to achieve it in SalesForce ? 

I want to display chatter to public, is this possible? Do i have to do a lot of coding in VF and APEX ? 

or

I want to make my community public, i,e., without actually logging in visitior should be able to see and traverse all the tabs available. Is this possible ? If so, how to achieve this ?